The Centers for Medicare & Medicaid Services (CMS) has issued an interim final rule with comment period revising the definition of multiple source drug for purposes of the Medicaid rebate program. By way of background, on July 17, 2007, CMS published a final rule with comment period that implemented provisions of the Deficit Reduction Act of 2005 pertaining to the Medicaid drug rebate program, including definitions concerning average manufacturer price, best price, single source drug, and multiple source drug. In that rule, CMS defined multiple source drug as a covered outpatient drug for which there is at least one other drug product which is rated as therapeutically equivalent, is pharmaceutically equivalent and bioequivalent, as determined by the Food and Drug Administration (FDA), and is sold or marketed in the United States during the rebate period. CMS is now revising this definition of multiple source drug to provide that the drug product is sold or marketed in the “State” during the rebate period, as opposed to sold or marketed in the “United States” during the rebate period. Further, CMS considers the drug to be sold or marketed in a State if it appears in a published national listing of average wholesale prices that CMS has selected provided the listed product is generally available to the public through retail pharmacies in that State. The rule is effective April 14, 2008; CMS will accept comments on the revisions until that date.